Mobile units, e.g. telephones, laptop computers, etc. are known to be able to roam in wireless networks between various locations. Still, while roaming through various networks and sub-networks they need to maintain their connectivity. Various aspects relating to this mode of operation were suggested by the IETF (“Internet Engineering Task Force”) and are described in a series of RFC (Request for Comment) documents.
As will be appreciated by those skilled in the art, one of the problems characterizing mobile networks is, that mobile nodes may replace rather frequently their respective traffic attachment points (as they are typically associated with the corresponding NAS) in the access network. This problem is more common for distributed networks, in which the network access server (NAS) may reside in any of the base stations associated with a specific network.
Various ways of overcoming this problem have been offered in the past For example our applications U.S. Ser. No. 11/175,384 (now U.S. Pat. No. 7,881,262) and Ser. No. 11/362,372 (now U.S. Pat. No. 7,561,692). The first describes a method for providing secured mobile IP services by creating a virtual anchored node at an ASN associated with the mobile terminal and with a logical NAS, and where the anchored node communicates when required with other elements associated with that ASN. U.S. Ser. No. 11/362,372 discloses a method for authenticating a mobile terminal by transmitting a request for authenticating the mobile terminal; receiving the request at a base station associated with the network at which the mobile terminal is operative; and selecting an entity that can operate as a single authentication access entity for that mobile terminal.
All acceptable solutions for mobile networking involve hiding the user mobility from the mobility unaware part of the network. Such hiding may be achieved for example by anchoring the mobile user's data path at a certain node within the mobility aware part of the network. The part of the data path between the anchor node and the mobile user's peer never changes due to the user's terminal mobility. This “Anchor Node” is typically referred to as Home Agent in Mobile IP networks and 3GPP2, GGSN in 3GPP networks.
However, it has later been recognized that mobile networking solutions should preferably include additional hierarchies of the data path anchoring. Mainly, because it is often desired not to overload the network with data related to terminal mobility within the access network (micro-mobility) form the remaining part of the mobile aware network. This may again be achieved by anchoring the data path within the access network in addition to the anchoring discussed above in the core mobile network. This type of solution is available in 3GPP, 3GGP2 and WiMAX_NWG architectures. In order to implement these solutions localized mobility management has also been addressed in the art such as in drafts of the Network-based Localized Mobility Management IETF Working Group, presented at http://www.ietf.org/html.charters/netlmm-charter.html.
Thus the data path anchoring described becomes hierarchical, consisting of one anchor point in the access network and one anchor point in the core network. This model has been further extended to allow more than two levels of hierarchy along the data path. Consequently, WiMAX NWG architecture allows having hierarchical data path where multiple ASN GWs serve as intermediate anchor points on the mobile user's data path extending between the serving BS and the anchor ASN GW/Foreign Agent.
Similarly, hierarchical MIPv4 is described in Mobile IPv4 Regional Registration Mobile IP Working Group Internet Draft, by Eva Gustafsson (Ericsson), Annika Jonsson (Ericsson), Charles E. Perkins (Nokia Research Center), which describes one additional level of hierarchy beneath the Gateway Foreign Agent (“GFA”).
The idea of having multi-level mobile data path hierarchies is now being recognized as a useful idea as it allows flexibility in localizing mobility within parts of mobile networks.
Still, the dilemma associated with hierarchical data path management, i.e. direct vis hierarchical data path for WiMAX NWG architecture is illustrated in FIG. 2. As may be seen from that Fig., the data path for an MS may be established either directly between the BS and ASN GW1 or alternatively through an intermediate anchor in ASN GW2. In general a hierarchical data path is considered to be a suboptimal solution from the routing perspective. However if the ASN IP Routing Segment 1 has much higher capacity than the ASN IP Routing Segment 2, it would be advisable to have an intermediate anchor in the ASN GW2, because in this case, the lower capacity routing segment will not have to accommodate transmission overheads associated with supporting handovers (as long as the mobile user moves between the base stations connected to the higher capacity routing segment).
In addition, US 2004063429 describes a configuration which comprises a number of routers and a gateway device connected above edge routers in order to provide in respective base stations a hierarchical structure and configured to perform relaying of data to the base stations, where the underlying idea of this publication is to make it feasible to readily decrease the handover transaction time.
However, the main unsolved problem associated with all the solutions discussed above, is, how to effectively manage such hierarchical data paths.